The first symptoms were non-stop vomiting and bloody diarrhea, the siblings’ parents posted on CaringBridge. After several trips to the ER, lab results revealed they had both suffered acute kidney failure.

Kallan’s parents later confirmed in a post on CaringBridge that their daughter had died, “Our sweet sweet little girl lost the battle. … Kade is still fighting.”

The pair visited a petting zoo the day they got sick, and a Minnesota health official confirmed to the Star Tribune that out of an “abundance of precaution” the facility quarantined the animals the Mareshes came in contact with. However, the zoo is just one of many potential E. coli sources, the official said.

According to the Centers for Disease Control, most E. coli are not dangerous and even play a role in a healthy digestive tract, but Kallan and Kade are suffering from a complication called hemolytic uremic syndrome.

Kade’s mother implored people to pray for her boy in a GoFundMe post. “Joe and I are so deeply hurt from sadness,” she wrote. “It is absolutely heart breaking watching your babies in so much pain and being so helpless.”